Agricultural implement with spring cushion for vertically adjustable subframe

Abstract

An agricultural implement has a main pull-type frame carrying a first set of ground-engaging tillage tools and a subframe carrying a second set of tillage tools. A lift mechanism including an hydraulic cylinder operated from the operator's position on the tractor pulling the implement adjusts the height of the subframe relative to the main frame to set the working depth of the tools on the subframe. A preload spring cushion mechanism is interposed between the main frame and the hydraulic cylinder to permit the subframe to lift for smaller obstacles and be reset by the spring without actuating the pressure relief valve. The force of the spring assists in resetting the subframe to its desired working depth after the obstacle is passed. In the illustrated embodiment, the spring cushion mechanism has an increasing moment arm as the spring compresses thereby to equalize the resetting force applied to the lift mechanism; and it is preloaded so that the operator can adjust the operating depth of the subframe. The hydraulic system includes a pressure relief bypass valve actuated at a predetermined pressure to permit fluid to flow between the rod and butt ends of the cylinder, permitting the cylinder to extend and the subframe to raise when a larger obstacle is encountered by the tools on the subframe.

We claim: 
     
       1. In an agricultural implement including a main frame adapted to be pulled by a tractor; a first set of tillage tools carried by said main frame; support wheel means for supporting said main frame; a subframe carried by said main frame; a second set of tools mounted to said subframe; subframe lift mechanism including an hydraulic cylinder connecting said subframe to said main frame for adjusting the elevation of said subframe relative to said main frame while maintaining said subframe generally parallel to said main frame, the improvement comprising: a spring cushion mechanism connected with said hydraulic cylinder between said main frame and subframe and including a spring, means for preloading said spring, a lever arm for compressing said spring when said second set of tools encounter an obstruction tending to lift said subframe, said spring compressing in response to said obstruction and acting to reset said subframe to its adjusted working depth after said obstruction is passed, and pressure-actuated hydraulic bypass valve means actuated at a predetermined fluid pressure for communicating the rod end of said cylinder with said butt end thereof, in response to an upward force on said subframe greater than a predetermined amount for permitting said cylinder to extend after said spring cushion mechanism has reached the limits of design operation. 
     
     
       2. The apparatus of claim 1 wherein said subframe lift mechanism includes a rock shaft journaled on said main frame; linkage means interconnecting said subframe with said rock shaft for effecting a four-bar linkage movement of said subframe relative to said main frame; a crank arm rigidly connected to said rock shaft and pivotally connected at its distal end to one end of said hydraulic cylinder; said lever arm of said spring cushion mechanism being pivotally connected at one end to the second end of said hydraulic cylinder and at its other end to said main frame for pivotal motion relative to said main frame. 
     
     
       3. The apparatus of claim 2 further comprising a stop means on said main frame for limiting the pivotal motion of said lever arm in one direction to limit the downward displacement of said subframe relative to said main frame for a given adjusted length of said hydraulic cylinder. 
     
     
       4. The apparatus of claim 3 further comprising a sleeve attached to said second end of said lever arm for journaling the same to said main frame; a spring bracket connected to said sleeve; a spring-abutment plate for fixing the position of one end of said spring; and a spring bolt having one end fixed to the movable end of said spring and its other end connected to said spring bracket for compressing said spring as said sleeve rotates in response to the rotation of said lever arm as said subframe is lifted. 
     
     
       5. The apparatus of claim 1 wherein said lever arm is pivotally connected to one of said frames at one end and said lever arm, pivotal connection and hydraulic cylinder are constructed and arranged such that the moment arm exerted by said lever arm to reset said subframe changes as the compression force on said spring increases thereby to equalize the resetting force applied to said subframe lift mechanism. 
     
     
       6. The apparatus of claim 5 characterized in that said moment arm increases as said spring force increases. 
     
     
       7. In an agricultural implement including a main frame adapted to be pulled by a tractor; a first set of tillage tools carried by said main frame; support wheel means for supporting said main frame; a subframe carried by said main frame; a second set of tools mounted to said subframe, the improvement comprising: subframe lift mechanism including an hydraulic cylinder and rigid four-bar linkage means for connecting said subframe to said main frame for adjusting the elevation of said subframe relative to said main frame while maintaining said subframe generally parallel to said main frame; a spring cushion mechanism connected with said hydraulic cylinder between said main frame and subframe and including a spring; means for preloading said spring and an arm for compressing said spring when said subframe is lifted; and pressure-actuated hydraulic bypass valve means actuated at a predetermined fluidpressure for communicating the rod end of said cylinder with the butt end thereof; said apparatus being constructed and arranged such that (a) for a predetermined initial range of upward force on said subframe, said hydraulic cylinder, linkage means and spring cushion mechanism are rigid, (b) for a predetermined range of greater upward force on said subframe sufficient to overcome said preload, said spring is compressed to permit said subframe to raise to clear smaller objects and to generate a reset force for said subframe, and (c) for a predetermined still larger upward force on said subframe, said valve means is actuated to permit said cylinder to change its length and thereby to enable said subframe to raise further and clear larger objects. 
     
     
       8. The apparatus of claim 7 further comprising a lever arm connected to said hydraulic cylinder and responsive to said reset force to change the moment arm through which said reset force is applied in such a manner as to compensate for increases in compression of said spring and equalize the reset force on said subframe. 
     
     
       9. In an agricultural implement including a main frame adapted to be pulled by a tractor; support wheel means for supporting said main frame; a subframe carried by said main frame; a set of tillage tools mounted to said subframe; subframe lift mechanism including an hydraulic cylinder connecting said subframe to said main frame for adjusting the elevation of said subframe relative to said main frame while maintaining said subframe generally parallel to said main frame, the improvement comprising: a spring cushion mechanism connected with said hydraulic cylinder between said main frame and subframe and including a spring, means for preloading said spring, a lever arm for compressing said spring when said set of tools encounter an obstruction tending to lift said subframe thereby to compress, said spring acting to reset said subframe to its adjusted working depth after said obstruction is passed, said spring, lever arm and hydraulic cylinder being constructed and arranged such that as said subframe is raised when said tools encounter an obstacle, said spring compresses while the reset moment arm through which the force of said spring is applied to reset said subframe increases thereby to equalize the reset force on said subframe even though the force of said spring increases. 
     
     
       10. The apparatus of claim 9 further comprising pressure-actuated hydraulic by-pass valve means actuated at a predetermined fluid pressure for communicating the rod end of said cylinder with the butt end thereof in response to an upward force on said subframe greater than a predetermined amount, thereby permitting said cylinder to change in length after said spring cushion mechanism has reached the limits of its operation.